When operating a vehicle at low temperatures (e.g., during engine cold-start), exhaust aftertreatment devices are not catalytically active enough to reduce engine emissions, such as hydrocarbons and oxides of nitrogen (NOx). In one approach, (e.g., U.S. Pat. No. 6,518,213), a three-way catalyst is deposited on a hydrocarbon trap positioned in an engine's exhaust, so that NOx is adsorbed by the three-way catalyst and hydrocarbons by the trap during low temperatures.
However, the inventors herein have recognized various issues with such an approach. For example, during low exhaust temperatures, such as during cold start, hydrocarbon and sulfur emissions may also be present in exhaust gases. Directly exposing a NOx adsorbing material (such as a three-way catalyst) to such emissions may foul the NOx adsorbing material, leading to degraded performance and an increase in NOx entering the environment. Further, a three-way catalyst may not be as effective at adsorbing NOx at low temperatures as a different NOx adsorber, such as a lean NOx trap.
Accordingly, as a brief summary, devices, systems and methods are disclosed for a hydrocarbon and NOx trap. In one example, a trap, such as a hydrocarbon and NOx trap, for reducing emissions from an engine, such as cold-start NOx emissions, includes a first, topmost layer, exposed to an exhaust gas flow path of exhaust gases from the engine, the first layer comprising a zeolite, a second layer, covered by the top most layer, the second layer comprising a NOx adsorbing material, and a monolithic substrate, directly supporting the second layer and indirectly supporting the first layer, the substrate providing a substantially rigid structure of the trap.
In this way, engine emissions, such as NOx and hydrocarbons may be adsorbed over the exhaust trap at low temperature and then thermally released, limiting cold start emissions beyond engines that only include a lean NOx trap. In one example, emissions are released when one or more further exhaust aftertreatment devices are warmed up and treating exhaust gas (e.g., oxidizing hydrocarbons and reducing NOx). Further, because the second layer is covered by the first layer, fouling of the NOx adsorbing material included in the second layer by hydrocarbons, sulfurous compounds and the like may be prevented.
It will be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description, which follows. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined by the claims that follow the detailed description. Further, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.